The diagnostic anchor in this patient was a laboratory finding rather than a physical sign: a strongly positive test for antibodies against U1 ribonucleoprotein, a component of the spliceosome, the cellular machinery that edits messenger RNA before proteins are made. High-titer anti-U1-RNP antibodies are the serological hallmark of mixed connective tissue disease, a systemic autoimmune disorder first described by Gordon Sharp and colleagues in 1972 that combines features of systemic lupus erythematosus, polymyositis, and systemic sclerosis. The condition is rare, with an estimated prevalence of roughly 3 to 37 per 100,000 people, and it disproportionately affects women. Yet the antibodies themselves can appear in patients whose disease never develops the full overlap picture, which is precisely what made this case so difficult to classify.

On admission, the clinical picture was alarming. Proximal muscle strength was graded 4 out of 5 in the deltoids and biceps but only 2 out of 5 in the hip flexors and quadriceps, meaning the patient could not raise her legs off the bed. Cranial nerves were intact, and crucially there was no rash, no Gottron’s papules, no heliotrope discoloration around the eyes, and no Raynaud phenomenon, the finger-whitening response to cold that typically signals connective tissue disease. The absence of these cutaneous and vascular stigmata is one reason the diagnosis eluded clinicians for so long. Inflammatory myopathy usually announces itself in textbooks with visible clues; here the disease confined itself almost entirely to muscle.

The laboratory numbers told a dramatic story. Serum creatine kinase, the enzyme that leaks into blood when muscle fibers rupture, measured 9,883 IU/L, roughly 68 times the upper limit of normal. Aldolase, another muscle enzyme, was similarly elevated at 75.6 U/L against a reference ceiling of 10. Inflammatory markers were high, with C-reactive protein at 116 mg/L, and the erythrocyte sedimentation rate at 67 mm/h. The extractable nuclear antigen panel revealed anti-U1-RNP antibodies at 17.67 U/mL, well above the positivity threshold of 5.0, while antibodies to Sm, Scl-70, and SS-B/La were negative and anti-dsDNA was merely equivocal, arguing against florid lupus. A positive direct Coombs test was noted but, without reticulocytosis, elevated lactate dehydrogenase, or low haptoglobin, could not be taken as proof of autoimmune hemolysis.

Electrodiagnostic testing added an important nuance. Nerve conduction studies were normal, excluding a neuropathy, but needle electromyography across ten muscles showed small, short-duration motor unit potentials with early full recruitment and, tellingly, no fibrillations or positive sharp waves. That non-irritable pattern is more characteristic of a chronic or so-called burnt-out myopathy than of florid active inflammation. The authors interpret it as the electrophysiological fingerprint of the six-year disease course, upon which the massively elevated creatine kinase indicated a fresh, biochemically active wave of muscle injury. Magnetic resonance imaging of the thighs corroborated the picture, showing diffuse T2 and STIR hyperintensity in the quadriceps consistent with muscle edema and inflammation, with no bone marrow abnormality to suggest a dystrophy or malignancy.

Treatment began within days. The patient received intravenous pulse methylprednisolone, 500 mg daily for three consecutive days, a high-dose regimen chosen because of the severity of weakness and the rapidly progressive pharyngeal dysphagia with its attendant aspiration risk. The response was rapid and unequivocal. By day four, swallowing had improved enough to restore safe oral intake, upper limb strength had returned to 5 out of 5, and lower limb strength had climbed to 4 out of 5 on the Medical Research Council scale. She was transitioned to oral prednisolone at 1 mg per kilogram per day, with methotrexate added as a steroid-sparing immunosuppressant alongside folic acid supplementation. At four-week follow-up, creatine kinase had fallen to 560 IU/L, approaching normal, and the dysphagia had not recurred.

Why did swallowing fail so suddenly? The report explains that oropharyngeal dysphagia in inflammatory myopathy arises when inflammation strikes the striated pharyngeal musculature, specifically the cricopharyngeus and the inferior pharyngeal constrictors, the muscles that coordinate the pharyngeal phase of swallowing. This feature is well recognized in polymyositis and dermatomyositis but underreported in mixed connective tissue disease, and it carries a grim prognosis when missed, being associated with aspiration, malnutrition, and death. Its abrupt emergence here, progressing from solids to liquids in roughly ten days, underscores why clinicians are urged to treat new dysphagia in any patient with myopathy as an emergency demanding immediate immunosuppression.

The classification question is where the case becomes genuinely instructive. Four sets of criteria, those of Sharp, Alarcón-Segovia and Villareal, Kasukawa and Miyawaki, and Kahn and Appeboom, are used to define mixed connective tissue disease, and all four require high-titer anti-U1-RNP antibodies. But each also demands at least one classic overlap manifestation beyond myositis: Raynaud phenomenon, swollen fingers or hands, synovitis, acrosclerosis, or sclerodactyly. This patient had none of them. Formally, therefore, she did not fulfill any of the four classification systems, and the authors designate her condition an anti-U1-RNP-positive inflammatory myopathy rather than definite mixed connective tissue disease. Such patients are increasingly viewed as occupying an early, incomplete, or myositis-dominant point on the disease spectrum, and a proportion evolve to meet full criteria over time, which is why the authors emphasize longitudinal surveillance rather than a fixed label.

The case also carries a lesson about anemia. Hematological abnormalities affect an estimated 30 to 40 percent of mixed connective tissue disease patients, and Coombs-positive hemolytic anemia has been described, yet this patient’s refractory microcytic anemia was attributed to iron deficiency for years despite supplementation failing. In retrospect, the authors write, that persistent anemia was a missed opportunity for earlier systemic evaluation. They recommend that any patient with proximal muscle weakness and unexplained, supplementation-resistant anemia undergo an autoimmune workup, including an extractable nuclear antigen panel and myositis-specific antibodies, early rather than late.

The authors acknowledge limitations: no muscle biopsy was performed to confirm the histological subtype, the burnt-out EMG pattern may simply reflect the prolonged delay, swallowing improvement was assessed clinically rather than by videofluoroscopy, and a broader myositis-specific antibody panel was not run. As a single case, the findings cannot be generalized to all populations. Still, the patient’s own account captures the stakes. She described years of declining function, sudden distress when swallowing failed, and relief at finally having a clear diagnosis after treatment restored her strength and her ability to eat normally. For clinicians, the message is blunt: autoimmune myopathy belongs on the differential for any longstanding unexplained proximal weakness, and the antibody that defines it is a simple blood test away.

Subject of Research: Anti-U1-RNP-positive inflammatory myopathy presenting with oropharyngeal dysphagia

Article Title: Anti‐U1‐RNP‐Positive Inflammatory Myopathy Presenting With Dysphagia: A Case Report

Article References: Anjlee, Rasheed, S., Ashfaq, M., Bai, S., Yaqubi, A. J., & Raza, A. A. (2026). Anti‐ U1 ‐ RNP ‐Positive Inflammatory Myopathy Presenting With Dysphagia: A Case Report. Clinical Case Reports, 14(10), Article e73676. https://doi.org/10.1002/ccr3.73676

Image Credits: AI Generated

DOI: 10.1002/ccr3.73676

Keywords: anti-U1-RNP antibodies, mixed connective tissue disease, inflammatory myopathy, dysphagia, myositis, creatine kinase, electromyography, methylprednisolone, autoimmune disease, anemia, rheumatology, case report